More particularly, but not exclusively, the invention concerns implementing known methods with the aid of a suitable probe for dosing oxygen by means of electronic paramagnetic resonance spectrometry of the lithium phtalocyanine molecule in its particular quadratic crystalline form. These known methods have been described in the documents FR-A-90 08738 and FR-A-90 08739 dated Jul. 10, 1990.
Mention shall first of all be made briefly to a population of nuclear or electronic spins being placed to be moved in rotation at a frequency Fo=.delta.Bo when they are subjected to a high and continuous magnetic induction Bo,.delta. being the characteristic gyromagnetic ratio of the substance in question. If in addition this polarized substance is subjected to an adjustable radiofrequency magnetic field having a direction perpendicular to the induction Bo, a resonance phenomenon is observed when this adjustable radiofrequency passes through the value Fo. This state of resonance is expressed by an emission or absorption of energy passing through maximums able to be detected.
Now, the molecular configuration of the quadratic crystalline form of the lithium phtalocyanine enables the latter to solely selectively trap the oxygen molecules 02. The trapped molecule 02 creates a magnetic coupling which affects the electric paramagnetic resonance signal of the phtalocyanine and allows for its spectrometric identification and accordingly for detecting the presence and measuring the quantity of oxygen molecules 02 in a gaseous mixture bathing a sample of lithium phtalocyanine. Furthermore, the phtalocyanines used in the invention are radical-like type phtalocyanines, this special characteristic implying that the width of their electronic paramagnetic resonance line varies almost linearly with the oxygen content in a range of oxygen concentrations of between 0 and 10%, which easily allows a quantitative dosing to be made.
The methods for detecting an electronic resonance signal are known to experts in this field and shall therefore not be described further in detail. In the present invention, any known method may be used and in particular the one described in the prior document FR-A-99 09830 dated Jul. 20 1988.
Nevertheless in theory, the passage through the state of magnetic resonance may be provoked, both by scanning the polarization induction Bo and also by varying the frequency of the excitation field. It is the first method which shall be described in the remainder of this text, but it needs to be understood that this is merely a non-restrictive option.
Although the principle of the detection of molecular oxygen by means of electronic paramagnetic resonance by lithium phtalocyanine has been known from the documents FR-A-90 08738 and FR-A-90 08739 dated Jul. 10, 1990, no embodiment of an industrial device has occurred since this date owing to the difficulties for designing an operational probe, especially as regards the introduction of the lithium phtalocyanine into the atmosphere to be tested, this introduction needing to be compatible with the possibility of precisely subjecting it to the magnetic inductions required for the production and detection of the electronic paramagnetic resonance phenomenon. Now, it is well known that the magnets and coils used for these purposes are extremely delicate to embody and are generally extremely expensive.